
Let \(T\) be a bounded linear operator acting on a separable infinite dimensional Hilbert space such that \(T\) is quasitriangular and the spectrum of \(T\) is connected. It is shown that for any \(\varepsilon > 0\) there exists a compact operator \(K\) with \(\|K\|< \varepsilon\) such that \(T+K\) is strongly irreducible. This result gives a partial answer to a question posed by D. A. Herrero.
Linear operator approximation theory, index, Quasitriangular and nonquasitriangular, quasidiagonal and nonquasidiagonal linear operators, Perturbation theory of linear operators, strongly irreducible, Weyl spectrum, quasitriangular, Linear operators defined by compactness properties, Spectrum, resolvent
Linear operator approximation theory, index, Quasitriangular and nonquasitriangular, quasidiagonal and nonquasidiagonal linear operators, Perturbation theory of linear operators, strongly irreducible, Weyl spectrum, quasitriangular, Linear operators defined by compactness properties, Spectrum, resolvent
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